Frequently, use is made of rectilinear light utilizing units in large apparatus so that, for example, the approach of the end of the tape is perceived at an early stage and the drive of the tape can be stopped by an auxiliary arrangement in good time.
In the case of apparatus of minimum size using replaceable mini-cassettes, use of such means has however serious difficulties. On the one hand, for sheer reasons of space, it is hardly possible to provide for a rectilinear light path from the light source through the magnetic tape. On the other hand, the use of reversing mirrors or the like which have to be separately installed in the cassette to provide for a labyrinthic path of the light beam at the appropriate places is not viable costwise.
It is an object of the present invention to provide means which will cater for a labyrinthic light passage even through a mini-cassette without additional trouble and expense. This problem is met in the present invention by the fact that the casing of the cassette is made of a reflective material, and that this casing has a projection which extends into the light path of the light utilizing unit and is provided with at least one reflecting surface which deflects the light beam from the light emitter to the light receiver after the position of the tape has been monitored. The flat or concave reflecting surface of the cassette casing, which may be made as an injection molding of a transparent material, can be produced actually during the injection molding operation in accordance with a further feature of the invention. The modern state of development of injection molding enables the reflecting surfaces in the cassette casing to be produced with an adequate degree of efficacy and on a large scale without difficulty and without additional expense in the course of the operation of injection molding the cassettes. A further result is that the passage of light from the light source within the cassette can be optimal.
The reflecting surfaces formed in accordance with the present invention can be used without retraction in any type of cassette construction and with any type of light unit, that is to say irrespective of whether the specific and critical position of the tape is identified by an aperture or reflecting surface on the tape. Moreover, the light aperture providing access to the light source can, for example, be controlled by a member monitoring the tape winding or by the tape winding itself.
A preferred embodiment of the invention is related to apparatus having a magnetic tape provided with two superimposed tracks in which each of these tracks can be brought into operation by reversing the cassette, and two light reflecting faces are arranged in the cassette casing in symmetrical disposition relatively to the reversing plane of the cassette so that a reflecting surface is made available to the elements of the light unit in each of the two positions of the cassette.